Acrylonitrile polymer composition stabilized with formaldehyde, an alkali sulfite and an inorganic acid and method of making same



United htates Patent ACRYLONITRILE POLYMER COMPOSITION STA- BILIZED WITHFORMALDEI-IYDE, AN ALKALI SULFITE AND AN INORGANIC ACID AND METHOD OFMAKING SAME Richard R. Holmes, Bethesda, Md., and Lloyd T. Jenkins,

Decatur, Ala., assignors to The Chemstrand Corporation, Decatur, Ala., acorporation of Delaware No Drawing. Application May 23, 1956 Serial No.586,669

17 Claims. (Cl. 260-326) This invention relates to the stabilization ofacrylonitrile polymers and blends thereof. More particularly, it relatesto the stabilization of acrylonitrile polymers and blends thereof whichhave a tendency to develop color upon standing or application of heat.

The term polymer, as employed in the instant description and claims, isintended to include homopolymers, copolymers, and blends thereof, saidpolymers, containing at least 80 percent by weight of polymerized orcopolymerized acrylonitrile in the polymer molecule.

Acrylonitrile polymers containing 80 percent or more of acrylonitrileare generally insoluble in the more common solvents. In those instanceswhere suitable solvents have been found, in order to effect solution,the application of heat is usually necessary. Where heat is employed toeffect solutions, from which shaped articles are to be formed, a tan todark brown color frequently develops in the solutions and therefore iscarried over into the product formed therefrom. This color also developsin solutions upon standing for prolonged periods of time.

The mechanism which causes color formation has not been definitelyascertained, although a variety of reasons therefor have been advanced.The presence of metal ions, such as iron, copper and manganese in thesolutions may cause the color. The employment of amide compounds assolvents may result in formation of amines when heat is applied andcause color in the compositions. Impurities present in the solvents havealso been cited as a cause. Whatever may be the reason for colorformation, it results in compositions and products of undesirablestandards and therefore, has been the source of concern, particularly incommercial operations where such types of polymers or copolymers areemployed.

Accordingly, it is an object of the present invention to preventundesirable color formation in acrylonitrile polymer compositions.

Another'object is to minimize color formation when solutions of theacrylonitrile polymers are permitted to stand for a prolonged period oftime or upon application of heat.

It is also an object of the invention to prevent color formation inacrylonitrile polymers at elevated temperatures.

A still further object of the invention is the production of solutionsof acrylonitrile polymers and articles pro duced therefrom havingimproved color characteristics.

Other objects and advantages will be apparent from a consideration ofthe description of the invention which follows hereafter.

In general, the objects of the invention are accomplished by dissolvingthe polymer of acrylonitrile in a suitable solvent therefor andpreventing or minimizing color form- "ice The components of theinhibiting agent may be employed in equal or unequal amounts, any oneconstituent being present in a range of from 98 to 1 percent in a threecomponent system. The total amount of inhibiting agent may be employedin a range of about 0.3 to 15 percent, based on the total polymerweight. However, it is preferred that the inhibiting agent of theinstant invention be present in a small amount compared to the amount ofpolymer dissolved. Thus, although the amount is not critical, it ispreferred that the inhibiting agent be present in the amount of about0.3 to 3 percent, based on the total weight of the polymer. Theinhibiting agent may be added to the solvents before or after thepolymer is dissolved therein. The inhibiting agent permits exposure tohigh temperatures for prolonged standing periods without the developmentof the objectionable color which usually results in such solutions. Thecompositions of the instant invention may be prepared in a varyingtemperature range. For example, the compositions of the instantinvention may be prepared by mixing the polymer, a suitable solvent andthe inhibiting agent at any temperature or heating the mixture to atemperature up to the boiling point of the solvent.

Among the acids which may be employed in practising the instantinvention are sulfuric acid, nitric acid, phos phoric acid, hydrochloricacid, etc.

Among the solvents which may be used in practising the instant inventionare N,N-dimethylformamide, N,N.- dirnethylacetamide, aqueous zincchloride, sulfuric acid, aqueous nitric acid, aqueous sodiumthiocyanate, ethylene carbonate, sulfolane, nitromethane, etc.

The polymeric materials, which may be employed in the practice of thepresent invention, are polyacrylonitrile, copolymers, including binaryand ternary polymers containing at least percent by Weight ofacrylonitrile in the polymer molecule, or a blend comprisingpolyacrylonitrile or copolymers comprising acrylonitrile with from 2 to50 percent of another polymeric material, the blend having an overallpolymerized acrylonitrile content of at least 80 percent by weight.While the preferred polymers employed in the instant invention are thosecontaining at least 80 percent of acrylonitrile, generally recognized asthe fiber-forming acrylonitrile polymers, it will be understood that theinvention is likewise applicable to polymers containing less than 80percent acrylonitrile and the same stability is realized with theinhibiting agents defined herein. The acrylonitrile polymers containingless than 80 percent acrylonitrile are useful in forming films, coatingcompositions, molding operations, lacquers, etc., inall of whichapplications the alleviation of undesirable color is extremelyimportant.

For example, the polymer may be a copolymer of from 80 to 98 percentacrylonitrile and from 2 to 20 percent of another monomer containing theC=C linkage and copolymerizable with acrylonitrile. Suitablemono-olefinic monomers include acrylic, alpha-chloroacryl'ic andmethacrylic acids; the acrylates, such as methylmethacrylate,ethylmethacrylate, butylmethacrylate, methoxymethyl methacrylate,beta-chloroethyl methacrylate, and the corresponding esters of acrylicand alpha-chloroacrylic acids; vinyl chloride, vinyl fluoride, vinylbromide, vinylid'ene chloride, 1-chloro-1-bromoethylene;methacrylonitrile; acrylamide and methacrylamide;alpha-chloroacrylamide, of monoalkyl substitution products thereof;methyl vinyl ketone; vinyl carboxylates, such as vinyl acetate, vinylchloroacetate, vinyl propionate, and vinyl stearate; N- vinylimides,such as N-vinylphthalimide and N-vinylsuccinimide; methylene malonicesters; itaconic acid and itaconic ester; N-vinylcarbazole; vinylfurane; alkyl vinyl esters; vinyl sulfonic acid; ethylene alpha,beta-dicarboxylic acids or their anhydrides or derivatives, suchasdiethylcitraconate, diethylmesaconate, styrene, vinyl naphthalene;"vinylsubstituted tertiary heterocyclic amines, such as the vinylpyridines andalkyl-substituted vinylpyridines, for example, 2-vinylpyridine,4-vinylpyridine, 2- methyl-S-vinylpyridine, etc.; l-vinylimidazole andalkylsubstituted l-vinylimidazoles, such as 2-, 4-, orS-methyll-vinylimidazole, and other C=C containing polymerizablematerials.

The polymer may be a ternary intetpolymer, for example, productsobtained by the interpolymerization of acrylonitrile and two or more ofany of the monomers, other than acrylonitrile, enumerated above. Morespecifi- Cathy, and preferably, the ternary polymer comprisesacrylonitrile, methacrylonitrile, and 2-vinylpyridine. The Zternarypolymers preferably contain from 80 to 97 percent of acrylonitrile, from1 to percent of a 'vinylpyridine for .a l-vinylimidazole, and from 1'to18 percent of another substance, such as methacrylonitrile or vinylchloride.

The polymer may also be a blend of polyacrylonitrile 'or of a binaryinterpolymer of from S0 to 99 percent acrylonitrile and from 1 to 20percent of at least one other C=C containing substance with from 2 to 50percent of the weight of the blend of a copolymer of from 10 to 70percent of acrylonitrile and from 30 to 90 percent of at least one otherC=C containing polymerizable monomer. Preferably, when the polymericmaterial comprises a blend, it will be a blend of a copolymer of 90 to98 percent acrylonitrile and from '2 to '10 percent of anothermono-olefinic monomer, such as vinyl acetate, which is not receptive todyestuff, with a :sufiicient amount of a copolymer of from 10 to 70percent er acrylonitrile and from 30 to 90 percent of a vinylsubstitutedtertiary heterocyclic amine, such as vinylpyridine or l-vinylimidazole,to give a dyeableblendhaving an overall vinyl-substituted tertiaryheterocyclic amine content of from 2 to 10 percent, based on the weightof the'blend.

'The polymers, useful in the practice of the present invention, may beprepared by any conventional polymeriza- "tion procedure, such as masspolymerization methods,

solution polymerization methods, or aqueous emulsion procedures.However, the preferred practice utilizes suspension polymerizationwherein the polymer is prepared in finely divided form for immediate usein the fiber fabrication operations. The preferred suspensionpolymerization may utilize batch procedures, wherein monomers "arecharged with an aqueous medium containing the necessary catalyst anddispersing agents. A'more desirable method involves the semi-continuousprocedure in which the polymerization reactor containing the aqueousmedium is charged with the desired monomers and the "continuouswithdrawal of polymer may also be employed.

The polymerization is catalyzed by means of any watersoluble peroxycompound, for example the potassium, ammonium and other water-solublesalts of peroxy acids, sodium peroxide, hydrogen peroxide, sodiumperborate, the sodium salts of other peroxy acids, and any otherwater-soluble compound containing a peroxy group '(O-O-). A widevariation in the quantity of peroxy compound is possible. For example,from 0.1 to 3.0 percent by weight of the polymerizable monomer may beused. The catalyst may be charged at the outset of the reaction, or itmay be added continuously or in incremerits throughout the reaction forthe purpose of maintaining a more uniform'concentration of catalyst inthe reaction mass. The latter method is preferred because "it 'te'nds'tomake the resultant polymer more uniform in "its chemical and physicalproperties.

Although the uniform distribution of the reactants throughout thereaction mass can be achieved by vigorous agitation, it is generallydesirable to promote the uniform distribution of reagents by using inertwetting agents, or emulsion stabilizers. Suitable reagents for thispurpose are thewater-soluble salts of fatty acids, such as sodium'oleate and potassium stearate, mixtures of water-soluble fatty acidsalts, such as common soaps prepared bythe saponification of animal andvegetable oils, the amino soaps, such as salts of triethanolamine anddodecylmethylamine, salts of rosin acids and mixtures thereof, thewater-soluble salts of half esters of sulfuric acid and long chainaliphatic alcohols, sulfonated hydrocarbons, such as alkyl arylsulfonates, and any other of a Wide variety of wetting agents, which arein general organic compounds containing both hydrophobic and hydrophilicradicals. The quantity of emulsifying agents will depend upon theparticular agents selected, the ratio of monomer to be used, and theconditions of polymerization. In general, however, from 0.01 to 1.0percent by weight of the monomers may be employed.

The emulsion polymerizations are preferably conducted in glass orglass-lined vessels which are provided with a means for agitating thecontents. Generally, rotary stirring devices are the most effectivemeans of insuring the intimate contact of the reagents, but othermethods may be successfully employed, for example by rocking 'ortumbling the reactors. The polymerization equipment generally used isconventional in the art and the adaptation of a particular type ofapparatus to the reaction contemplated is within the province of oneskilled in the art. The articles manufactured therefrom may be producedby well-known conventional methods, for example, the wetspinning,dry-spinning and melt-spinning methods for producing fibers.

The following examples are illustrative rather than limitative and allparts, proportions and percentages are by weight unless otherwisespecified.

EXAMPLE I of titanium dioxide. The mixture was stirred and heated to 'C.It was then quickly cooled to room temperature and the color measured.This sample was used as a control. The purity is set forth below.Subsequently, like samples were prepared but with 0.225 gram of a colorinhibitor containing 0.075 gram each of formaldehyde, sodiumhydrosulfite and sulfuric acid; and formaldehyde, sodium bisulfite andsulfuric acid. The

purity is set forth below.

Table l Inhibitor Percentage Purity Used Control. 7X0

Formaldehyde, Sodium Hydrosulfite and Sulfuric Acid. '3 318Formaldehyde, Sodium Bisulfite and Sulfuric Acid 3 4.3

EXAMPLE II 7.5 grams of a copolymer containing 94 percent .ofacrylonitrile and 6 percent of vinyl acetate were added to 45milliliters of N,N-dimethylacetamide containing approximately 0.05 gramof titanium dioxide. The mixture was stirred and heated for 35 minutesat 70 "C. It was then quickly cooled to room temperature and the colormeasured. This sample was used as a control. The purity is set forthbelow. Subsequently, like samples were prepared but with 0.225 gram ofan inhibiting agent containing 0.075 gram each of formaldehyde, sodiumhydrosulfite and sulfuric acid; and formaldehyde, sodium bisulfite andsulfuric acid. The .purity .is set forth below.

Table II Inhibitor Percentage Purity Used Control..- 10.2 FormaldehydeSodium Hydrosulfite and Sulfuric Acid 3 3.9 Formaldehyde, SodiumBisulfite and Sulfuric Acid 3 7.3

EXAMPLE III purity is set forth below. a Table III Inhibitor PercentagePurity Used Control 8. 5 Formaldehyde, Sodium Hydrosulfite and SulfuricAci 2.0 Formaldehyde, Sodium Bisulfite and Sulfuric Acid 4. 9

The alkali metal salts and zinc salts of sodium hydrosulfitc whenemployed in practising the present invention will give the same resultsas sodium hydrosulfite with respect to the purity readings as set forthabove.

The tests for color indicative of approaching whiteness used throughoutthe examples consist of measurements of purity as calculated from thetristimulus values determined on a General Electric Spectrophotometer bythe methods recommended by the Standard Observer and Coordinate Systemof the International Commission on Illumination, as fully set forth inthe Handbook of Colorimetry published by The Technology Press,Massachusetts Institute of Technology in 1936.

The compositions of the instant invention present many advantages. Forexample, products formed from the polymer solutions of the instantinvention are free of objectionable color and therefore of greatercommercial value. In preparing the polymer solutions, heat may beapplied without the danger of color formation and the solutions, ifnecessary, may stand for prolonged periods and remain free of color. Theinhibiting agents are readily available and inexpensive. Therefore, nogreat increase in production cost is necessary. The compositionscontaining the inhibitors may be prepared without going through detailedand elaborate procedures that necessitate expensive changes in thedesign of the apparatus used to manufacture them.

It will be understood to those skilled in the art that many apparentlywidely different embodiments of this invention can be made withoutdeparting from the spirit and scope thereof. Accordingly, it is to beunderstood that this invention is not to be limited to the specificembodiments thereof except as defined in the appended claims.

We claim:

1. A new composition of matter comprising a polymer containing at least80 percent of polymerized acrylonitrile and up to 20 percent of anotherpolymerizable mono-olefinic monomer copolymerizable therewith, a solventtherefor, and an inhibiting agent containing substantially equalproportions by weight of formaldehyde, a compound selected from thegroup consisting of sodium hydrosulfite and sodium bisulfite; and. aninorganic acid having an ionization constant greater than 1x 10".

2. A new composition of matter as defined in claim 1 wherein the polymeris a copolymer containing from to 98 percent of acrylonitrile and from 2to 20 percent of another polymerizable mono-oleiinic monomercopolymerizable therewith.

3. A new composition of matter as defined in claim 1 wherein the polymeris a blend of 80 to 99 percent of (A) a copolymer containing to 98percent of acrylonitrile and 2 to 10 percent of vinyl acetate and l'to20 percent of (B) a copolymer containing 10 to 70 percent ofacrylonitrile and 30 to 90 percent of 2-methyl-5- vinyl pyridine.

4. A new composition of matter as defined in claim 1 wherein the polymeris polyacrylonitrile.

5. A new composition of matter as defined in claim 1 wherein theinhibiting agent contains formaldehyde, sodium hydrosulfite and sulfuricacid.

6. A new composition of matter as defined in claim 1 wherein theinhibiting agent contains formaldehyde, sodium bisulfite and sulfuricacid.

7. A new composition of matter as defined in claim 1 wherein the solventis N,N-dimethylacetamide.

8. A new composition of matter comprising a polymer blend of(A) acopolymer containing 90 to 98 percent of acrylonitrile and 2 to 10percent of another polymerizable mono-olefinic monomer and (B) acopolymer containing 10 to 70 percent of acrylonitrile and 30 to 90percent of a vinyl substituted tertiary heterocyclic amine, said blendhaving an overall vinyl substituted tertiary heterocyclic amine contentof from 2 to 10 per cent based on the weight of the blend, a solventtherefor, and an inhibiting agent containing substantially equalproportions by weight of formaldehyde, a compound selected from thegroup consisting of sodium hydrosulfite and sodium bisulfite; and aninorganic acid having an ionization constant greater than 1X 10".

9. A new composition of matter comprising a copolymer containing 80 to98 percent of acrylonitrile and 2 to 20 percent of vinyl acetate, asolvent therefor, and 0.3 to 15 percent, based on the total weight ofthe polymer, of an inhibiting agent, said inhibiting agent containingsubstantially equal proportions by weight of formaldehyde, a compoundselected from the group consisting of sodium hydrosulfite and sodium.bisulfite; and sulfuric acid.

10. A new composition of matter comprising a polymer blend of 80 to 99percent of (A) a copolymer containing 90 to 98 percent of acrylonitrileand 2 to 10 percent of vinyl acetate and 1 to 20 percent of (B) acopolymer containing 10 to 70 percent of acrylonitrile and 30 to 90percent of 2-methyl-5-vinyl pyridine, a solvent therefor, and 0.3 to 15percent, based on the total weight of the polymer, of an inhibitingagent, said inhibiting agent containing substantially equal proportionsby weight of formaldehyde, a compound selected from the group consistingof sodium hydrosulfite and sodium bisulfite; and sulfuric acid.

11. A new composition of matter comprising a polymer containing at least80 percent of polymerized acrylonitrile and up to 20 percent of anotherpolymerizable mono-olefinic monomer copolymerizable therewith, a solventtherefor, and 0.3 to 15 percent, based on the total weight of thepolymer, of an inhibiting agent, said inhibiting agent containingsubstantially equal proportions by weight of formaldehyde, a compoundselected from the group consisting of sodium hydrosulfite and sodiumbisulfite; and sulfuric acid.

12. A method for preparing a new composition of matter comprising mixinga polymer containing at least 80 percent of polymerized acrylonitrileand up to 20 percent of another polymerizable mono-olefinic monomercopolymerizable therewith, a solvent therefor, and an inhibiting agentcontaining substantially equal proportions the group consisting ofsodium hydrosulfite and sodium ,bisulfite; and an inorganic acid havingan ionization constant greater than 1 l0- and "heating the mixture toform a homogeneous solution.

13. The method as defined in claim 12 wherein the polymer is a copolymercontaining from 80 to 98 percent of acrylonitrile and from 2 to 20percent of another polymerizable mono-olefinic monomer copolymerizabletherewith.

14. The method as defined in claim 12 wherein the polymer is a blend of80 to 99 percent of (A) a copolymer containing 90 to 98 percent ofacrylonitrile and 2 to percent of vinyl acetate and 1 to 20 percent of(B) a copolymer containing 10 to 70 percent of 'acrylonitrile'and 30 to90 percent of 2-methyl-5-vinyl pyridine.

15. The method as defined in claim 12 wherein the polymer ispolyacrylonitrile.

16. A method for preparing a new composition of matter comprising mixinga copolymer containing 80 to 98 percent of acrylonitrile and 2 to 20percent of vinyl acetate, a solvent therefor, and 0.3 to 15 percent,based on the total weight of the polymer, of an inhibiting agent, saidinhibiting agent containing'substantially equal proportions by weight offormaldehyde, a compound selected from the group consisting of sodiumhydrosulfite and sodium bisulfite; and sulfuric acid, and heating themixture to a temperature in 'a range of 25 C. to the boiling point ofthe mixture to form a homogeneous solution.

17. A method for preparing a new composition of .matter comprisingmixing a polymer blend of to 99 percent of (A) a copolymer containing to98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate and 1to 20 percent of (B) a copolymer containing 210 to 70 percent ofacrylonitrile and 30 to 90 percent of 2- methyl-5-vinylpyridine, asolvent therefor, 0.3 to 15 percent, based on the total weight of thepolymer, of an inhibiting agent, said inhibiting agent containing sub--stantially equal proportions by weight of formaldehyde,

a compound selected from the group consisting of sodium hydrosulfite andsodium bisulfite; and sulfuric acid, and heating the mixture to atemperature in a range of 25 C. to the boiling point of the mixture toform a homogeneous solution.

References Cited in the file of this patent UNITED STATES PATENTS2,502,030 Scheiderbauer Mar. 28, 1950 2,514,363 Banes July 11, 19502,677,675 Nagy May 4, 1954

1. A NEW COMPOSITION OF MATTER COMPRISING A POLYMER CONTAINING AT LEAST80 PERCENT OF POLYMERIZED ACRYLONITRILE AND UP TO 20 PERCENT OF ANOTHERPOLYMERIZABLE MONO-OLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, A SOLVENTTHEREFOR, AND AN INHIBITING AGENT CONTAINING SUBSTANTIALLY EQUALPROPORTIONS BY WEIGHT OF FORMALDEHYDE, A COMPOUND SELECTED FROM THEGROUP CONSISTING OF SODIUM HYDROSULFINE AND SODIUM BISULFITE; AND ANINORGANIC ACID HAVING AN IONIZATION CONSTANT GREATER THAN 1X10-4.